Captive panel fasteners are well known in the industry. One type of fastener is arranged so that an internally threaded stud nut is held in position extending through an opening in a panel, with the internally threaded end of the stud extending through the panel. When large panels with many fasteners are used, it is important that the fasteners be properly held in position ready for the securing of their internally threaded ends to a fastener receptacle or other threaded member.
With regard to such fasteners, reference to U.S. Pat. No. 4,655,658 issued Apr. 7, 1987 to Gulistan, is useful. This patent discloses an externally threaded captive panel fastener wherein the fastener is held in position extending through a hole in a panel, by a washer. The washer has inwardly extending prongs which fit into longitudinally extending slots running through the fastener's threaded surface. The washer is retained on the fastener, and hence the fastener is retained on the panel, by an outwardly extending lip or wall at the outer end of the fastener which blocks the ends of the slots and prevents the washer from sliding off the fastener. It was originally intended that the slots of the Gulistan invention could be formed by milling or grinding. However, that proved impractical because of damages to the threads. Currently, the slots are formed by an EDM process involving the removal of material by an electrode in a special bath.
Though the EDM process is expensive, the type of EDM process used in forming the slots on the fastener described in the Gulistan patent is less expensive than the EDM process used in forming the slots on such fasteners as that described in U.S. Pat. No. 4,747,738, issued May 31, 1988 to Duran. The slots on the Gulistan fastener are less expensive to form because they extend all the way to the end (opposite of the head) of the fastener. In the Duran type fastener, the slot must end with a sharply defined wall. Forming the sharply defined wall requires a more difficult and expensive EDM process than the slots on the Gulistan fastener require.
One aspect of such externally threaded captive panel fasteners as described in Gulistan and Duran is that the outer diameter of the retaining lip is constrained to be within the root diameter of the threads so as to not interfere when the fastener is threaded into a tapped hole or the like. This constraint on the deformed end wall outer diameter imposes a relatively tight dimensional tolerance on the fasteners. This in turn requires extra care in the fabrication of such fasteners thereby increasing their cost Furthermore, the constraint on the upper limit to the outer diameter of the deformed end wall may result in a fastener whose washer retention strength is less than that which is desired.
Accordingly, an important object of the present invention is to provide a captive panel fastener that is easier and therefore less costly to produce, and which may provide greater washer retention strength.
Another aspect of the externally threaded fastener of U.S. Pat. No. 4,655,658 is that the forming tool for outwardly deforming the end wall of the fastener includes two components, one of which operates from within the opening in the end of the fastener, while the other is threaded to the fastener's external threads. However, in the case of an internally threaded fastener, it would appear, from an initial consideration of the geometry involved, that it would not be practical to deform the end wall outwardly, since the threaded portion of the tool would be in engagement with the fastener's internal threads thereby occupying the space needed to operate the portion of the tool used to deform the end wall. Accordingly, another object of the present invention involves overcoming this apparent problem.
Additionally, a further aspect of captive panel fasteners is that, when in the captured position but prior to being joined to an appropriate joining member, the captive fasteners ordinarily extend through and protrude from the panel or other surface in which they are captured. This geometry may result in assembly and alignment problems when the panel or other surface to which attachment is to be made is large or unusually shaped or curved.
Accordingly, a further object of the present invention is to provide a captive panel fastener which, when in the captured position but prior to being joined to an appropriate joining member, is prevented from protruding outward from the panel or other surface in which it is captured.